Conventionally clamp-type ammeter is used to measure the current flowing in the wire. A clamp-type ammeter presents a substantially annular shape and accommodates current sensors in each of one side holder portion and the other side holder portion disposed opposite to each other, and has a structure which openably mounts on the instrument body one side sensor and the other side sensor comprising a joining end contacting with each other when closing (Patent Literature 1).
The clamp-type ammeter leads the magnetic field generated by current flowing through the electric wire to a current sensor such as a Hall element, by surrounding (clamping) the electric wire through which current flows with one side sensor portion and the other side sensor portion which are openably constituted.